The present invention relates to a method for controlling relative movement between a recording medium and a sensor array when information is sequentially read by moving the sensor array relative to the information recording medium. More particularly, the present invention relates to a method for controlling a recording medium and a reproducing head when an information track of an information recording medium is optically focused onto a sensor array and a bit pattern linearly recorded on the information track is read.
Recently, many types of optical recording and reproducing apparatus which use information recording media, such as optical files or compact disks have been proposed. A card-like optical information recording medium (optical card) which is easier to carry than such information recording media, and which has a large capacity relative to its size, has also been proposed.
FIG. 1(a) shows a schematic plan view of a record format of the optical card, and FIG. 1(b) shows a partial enlarged view of the record format.
In FIGS. 1(a) and 1(b), a record area 2 is provided on an optical card 1 which is the information recording medium. The record area 2 has a plurality of bands 3 arranged thereon. Each of the bands 3 has a plurality of tracks 4 arranged thereon, and each of the tracks 4 comprises information tracks 4a having an information capacity of several tens to one hundred bits, and a portion of a reference line (R line) 5 which delimits the bands 3. An arrow A indicates a direction of movement of the optical card 1 in a reproduction mode, and an arrow C indicates a direction of scan for reading information by the optical head in the reproduction mode.
FIG. 2 shows a diagram of the optical card reproducing apparatus, and FIG. 3 illustrates an operation of the reading head.
In FIGS. 2 and 3, the optical card 1 is movable in the direction A by a rotation mechanism 6. The information recorded on the optical card 1 is read and reproduced by the optical head 11 for each of the tracks 4. A light from a light source 7, such as an LED, is focused by an illuminating optical system 8 and irradiated as a spot onto the track 4 on which information has been recorded. The image on the track 4 is focused onto a sensor array 10 by a focusing optical system 9 so that an electrical signal representing the information recorded on the track 4 is produced by the sensor array 10. After the reading of the track 4, the optical card 1 is moved in the direction A and the optical head 11 is moved in the direction C so that the information on the next track is read in a similar manner.
FIGS. 4(a) and 4(b) show reading areas on the optical card by the sensor array.
In FIG. 4(a), the direction of arrangement of information on the information track 4a of the optical card 1 and the longitudinal direction of the read area 17 by the sensor array 10 are parallel, and in FIG. 4(b), the direction of arrangement of information and the longitudinal direction of the read area 17 are not parallel.
Usually, when the optical card 1 is to be loaded to the optical card reproducing apparatus, the direction of arrangement of the tracks (arrow E) of the information tracks 4a and the direction of movement of the optical card 1 (arrow A in FIG. 2) are not parallel, because of positional deviation when the optical card is loaded or abrasion of the optical card 1. Namely, as shown in FIG. 4(b), the longitudinal direction of the read area 17 of the sensor array 10 and the direction of arrangement of the information track 4a (arrow D) are not parallel but have an angle .theta. therebetween. As a result, when the optical card 1 is moved in the direction A in the reproduction mode, the information track 4a deviates from the illumination spot irradiated to read information from the track, in the direction C. If the angle .theta. is relatively large, the information track 4a moves off the illumination spot and information cannot be reproduced.